The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
In a vehicle, there are multiple devices that utilize a friction plate, i.e., a clutch, to rotatably interconnect members thereby transferring torque from one device to another. A gear ratio selectable transmission transfers torque from a torque machine, such as an engine or motor, to a driveline for providing motive force for the vehicle. The transmission provides several gear ratios to increase or decrease the amount of torque delivered to the driveline.
Transmissions may have manually selectable gears, typically referred to as a manual transmission, or automatically selected gears typically referred to as an automatic transmission. In a vehicle equipped with a manual transmission, a vehicle operator is able to disengage the clutch while selecting a forward or reverse gear. After a gear is selected, the operator releases the clutch pedal to engage the rotating assembly thereby transferring the torque produced by the motor to the driveline. Automatic transmissions are typically hydraulic fluid driven and have a fluid coupling, typically referred to a torque converter, in place of the clutch and are controlled by a control module. Automatic transmissions typically are less efficient due to viscous and pumping losses. A third type of transmission is known and is typically referred to as a semi-automatic transmission. The semi-automatic transmission can be an automated manual transmission or a dual clutch transmission with at least one clutch but activation and gear selection can be operated hydraulically, electronically, or electro-hydraulically as controlled by a control module. The automated manual transmission has a single clutch and is a similar configuration as the manual transmission. The dual clutch transmission includes two clutches with one clutch able to select odd gear sets and the other clutch able to select even gear sets. The control module is capable of selecting a preferred operating gear ratio and automatically shifting into the selected gear. The control module may also accept inputs from the operator as to when to select and what gear selection should be made and performs the gear change as commanded.
The semi-automatic transmission may be either a wet clutch, one in which a transmission fluid is maintained around the clutch, or a dry clutch, one without fluid. A wet clutch will typically be used to provide a smoother clutch engagement, higher power density, and longer slip, while a dry clutch can provide a higher efficiency. The semi-automatic transmission, either wet or dry clutch, typically provides higher efficiency than the manual and automatic transmissions. However, the application of the clutch can provide noticeable feedback through the driveline as the clutch becomes engaged with the flywheel. The feedback occurs as an output torque variation due to the friction material and steel surface friction interface experiencing a stick-slip occurrence, commonly referred to as shudder. Shudder occurs most frequently after a period of use due to contamination. In the case of a wet clutch, shudder will be more likely to occur when the fluid degrades.